What usually has to fit in 20 KB
A 20 KB limit is small. On application forms it most often applies to a signature, a left thumb impression, or a small photograph that only has to show a face. Some forms put a separate, larger limit on the photo and keep 20 KB for the signature, so read the line next to each upload button. Whatever the limit is for, it is about the file on disk, not the size it looks on screen.
For comparison, a photo straight from a phone camera is typically 2 to 5 MB, a hundred times or more over 20 KB. Getting there takes both a lower JPG quality and fewer pixels, and this page does both in the right order.
Signature under 20 KB: get a clean scan first
- Sign with a black or dark blue pen on plain white paper. Thin ballpoint lines can disappear when compressed; a gel pen or felt tip holds up better.
- Photograph it flat, in daylight, without your shadow over the page.
- Crop tightly around the signature before you drop it here. A wide strip of paper costs bytes and makes the signature small on the form.
A white background compresses to almost nothing, so a cropped signature usually fits in 20 KB at a high quality and at a good width. If the form asks for a pixel size such as 140 x 60, type it under Width and height.
Photo under 20 KB
A face needs more bytes than a signature. At 20 KB a photo of about 300 x 400 pixels keeps a clear face at a medium JPG quality, which is more than most forms display. Crop to head and shoulders first: the page then spends the 20 KB on the face rather than the room behind it. A plain, light background also helps, both for compression and because many forms ask for one.
Convert image to JPG at 20 KB
The format is set to JPG on this page because nearly every form accepts it and it gives the best quality at a small size. A PNG, WebP or AVIF you choose is converted as part of the same step. Transparent areas in a PNG become white, which is what a signature on a form should look like anyway.
If it comes out too small
Some forms ask for a signature between 10 and 20 KB, and a simple signature can compress well under 10 KB. Use increase image size in KB with 10 KB as the minimum; it raises the quality honestly and lands just above 10 KB, so the file stays under 20 KB.
Need a different number? Reduce image size in KB takes any limit, and compress image to 50 KB covers the larger photo limit many forms set alongside the signature. Every image tool runs in your browser, and the image never leaves your device.
The image is redrawn with your browser's own canvas, so the result depends on the browser's JPG, PNG and WebP encoders. MDN's image file type guide explains which format suits photos, signatures and scans.